In a conventional laser oscillator, in order to generate laser light having excellent isotropy from a laser medium having anisotropy or inhomogeneity in gain distribution, an image rotating optical system is constituted with a plurality of mirrors provided in a light path inside an optical resonator. The intensity distribution of the laser light is thereby rotated to a desired angle around an optical axis while the laser light passes through the laser medium. Consequently, the anisotropy of the gain distribution can be compensated to generate the laser light having excellent isotropy (See Patent Document 1).
In a conventional laser amplifier, an inversion optical system is constituted with orthogonal mirrors, and a light beam is spatially inverted, thereby reducing the effect of the asymmetry property of the laser medium (See Patent Document 2).